R o u t i neT e st ingo fB a l an ce s SOP for Periodic Eccentricity Tests (Routine Tests) Title: SOP for Periodic Eccentricity Tests Document No.: Author: METTLER TOLEDO Laboratory & Weighing Technologies Number of Pages: 4 Controls Replacement Document: N/A Reason for Revision: N/A Release Date: 17. Oct. 2007 Release for Routine OperationReviewed by:Date:Signature:Approved by:Date:Signature:R o u t i n e T e s t i n g o f B a l a n c e s General Basic Rules for Handling Balances • Before using a balance, make sure the balance was left on power for a sufficient period of time (men-tioned in the balance operating instructions).• Make sure the balance is leveled.• Minimize environmental influences, e.g. open windows, direct sunlight or strong drafts.• Do not enter the draft shield with hands. Use gloves or long tweezers.• Place objects gently on the pan.Basic Rules for Handling Weights Test Weights • Only an external test weight with calibration certificate can make a balance a “traceable” piece of equip-ment.• Test weights should always be placed gently on a clean weighing pan and put back immediately in their storage place after use.• Test weights (since they are also part of measuring equipment) need to be re-calibrated at specified inter-vals (ISO 9001).• Any incident, which might have affected the value of the test weight, should trigger an immediate re-cali-bration. METTLER TOLEDO’s calibration services will give advice on this.How to Store Test Weights• Test weights should be stored in their original box.• Test weights should be stored in the same room as the balance they are used with, since temperature dif-ferences between test weights and their surrounding lead to measurement errors.• Test weights that have not been stored at the same temperature need acclimatization, which can take sev-eral hours.How to Move Weights• Test weights should only be handled with appropriate tools such as tweezers, forks, handles or gloves (see METTLER TOLEDO’s accessories for weights).• These tools should be exclusively used for transferring test weights, to avoid possible contamination.Eccentricity TestPreparation• Before the test is performed, the test weight must be acclimatized to the ambient temperature of the bal-ance.• Prepare a sheet to note the readings of the eccentricity test.Test Procedure• Place the test weight in the center (1) of the pan and tare (if required press zero)• Place the test weight on position 2 at “Left front”Note: Move the weights by lifting them; do not shift weights on the pan• Read the stable value from the display and note it• Repeat the measurements on positions 3, 4 and 5.Evaluation• The largest reading (positive or negative) of any of the 4 corners (2 to 5) is the eccentric load deviation.• Evaluate whether the eccentric load deviation exceeds the defined “Warning Limit” 1).• Evaluate whether the eccentric load deviation exceeds the defined “Control Limit” 2).DeviationWarning Limit 1) (where defined)• If the warning limit is exceeded, level the balance and repeat the test.• If the warning limit is exceeded again, report that the warning limit was not met to the laboratory supervi-sor or the person responsible of the balance. Optionally, contact METTLER TOLEDO’s service organization for advice.Control Limit 2)• If the control limit is exceeded, report the problem to the laboratory supervisor or the person responsible of the balance.• Mark the balance as “out of control limits”.• Contact METTLER TOLEDO service organization for advice.1) – Values within the warning limit: No action is necessary.– Values between the warning and control limit are within the tolerance but must be kept under surveillance. Corrective action may be appropriate, depending on the direction in which the values are changing.2) – Values within the control limit, see 1)– Values beyond the control limit show that weighing process is no longer under control and immediate action is therefore required.Mettler-Toledo AGLaboratory & Weighing Technologies Im LangacherP.O. Box LabTecCH-8606 Greifensee Switzerland /GWPFor more information。
微量称量指微量称量效率南最大限度提高提高结果质量确保操作更安全10 个步骤微量称量指南2310 个步骤实现成功的微量称量实用称量指南1. 哪款微量天平适合我？ 42. 应当将微量天平放置到哪里？ 63. 为什么说微量天平校准非常重要？ 74. 如何确保日常称量的准确结果？ 85. 如何处理漂移的称量结果？ 96. 如何优化操作微小的样品？ 107. 如何更轻松地清洁微量天平？ 118. 如何提高称量过程的效率？139. 可使用哪些数据采集 / 数据传输方法？ 1410. 优化微量称量的其他有用技巧154微量称量指南1. 哪款微量天平适合我？测量不确定度 [%]重量 [g]最大准确度限值：最小称量值最小净重客户的过程允差 [%]图 1：一台典型超微量天平的典型测量不确定度曲线。
达到准确度极限值时，相对测量不准确度会随着样品重量的下降而升高，可超过用户定义的允差。
黄色区域代表用户所得最小净重与准确度限值之间的安全边际。
考虑在选择适合于您需求的天平时的相关标准。
在任何天平上进行的每一次测量都具有不确定性。
了解这种不确定性对于确保准确的称量结果和避免下游处理时出错至关重要。
对于微量天平而言，不确定度几乎完全与称量微小样品时的重复性（精确性）有关（即：在特定天平的小量程段）。
决定称量仪器准确性的不是可读性，而是重复性或最小称量值。
为了找到适合您需求的微量天平，您应当明确想要称量的最小量以及所需称量准确性（即：允差）。
在掌握这些基本信息之后，便可确定所需微量天平的准确性。
您的称量顾问可帮助您对此进行计算和确认其符合您的日常需求。
5示例• 通常称量的最小样品（由用户定义）。
（最小净重 = 2 mg ） • 所需允差 = 2 mg ± 10 ŞI [= 0.5%]建议对于此类应用，建议使用微量天平。
一台分析天平的重复性为 7 µg ，但对于此项任务而言准确性不够高，而一台重复性为 0.15 I 的超微量天平可根据要求称量极为少量的样品，但可能不被需要。
白皮书电白皮书1. 介绍以下示例描述了在许多实验室经常发生的情形：分析天平通常用于将预定量的粉末加入玻璃烧杯，以制备特定浓度的溶液。
例如，将 100ml 的容量瓶放置在秤盘上。
一般情况下，烧杯上可能会产生静电荷，因此在称量容器内诱发补充电荷。
这会导致产生净引力。
该净引力可将烧杯拉下，使之显得重于实际质量；或者会将其向上推，使之变得更轻。
在干燥空气状况下或者空气控制的环境中，例如典型的分析实验室，通常更容易产生电荷，从而导致更大的误差源。
如果天平显示稳定的称量值，则用户通过天平去皮和手动粉末加样继续操作，这是个苛刻、相对耗时的步骤。
任一方向的净引力都会使用户加入过多或过少的粉末，从而导致错误的最终溶液浓度。
一个典型的示例是，去皮容器上的电荷在一定时间内缓慢地释放至特定环境内，使用户继续添加过多的粉末，从而导致更大的称量误差。
最终溶液浓度将变得非常高，在某些分析测量条件下可产生明显的效果，导致超差 (OOS) 结果，甚至大量的重新测试工作。
称量少量样品加入大玻璃容器或塑料容器中，这是静电荷显著增加称量结果误差的典型情况。
2白皮书梅特勒-托利多3白皮书梅特勒-托利多图 1：显示测量烧杯上的正电荷和天平外壳上的补充负电荷之间的场力线。
电势差导致天平和待称材料之间产生力。
该排斥力的垂直分量增加了质量，从而影响称量结果。
1) 无摩擦也可产生电荷。
只需分离两种不同的材料（即：将玻璃烧瓶从玻璃表面取下）便足以产生电荷。
电荷越强，摩擦电序中的材料分离越明显。
2. 静电荷的物理效果 - 何时的条件特别关键？ 2.1 静电力库仑定律 [1] 指出电荷施加的相互作用力 F E 表示为：F E = 1 Q 1 Q2 或者简化为 F E = k e Q 1 Q 2 [1]4ʌİ0İr r 2r 2其中：k e 是库仑常数Q 代表两个物体上的单独电荷r 是物体之间的距离İ0 & İr 是绝对和相对介电常数2.2 称量过程中的静电力天平或待称材料/容器上的电荷会产生静电力。
